The present invention relates to a clamp well suited for use as a jig whereby materials of assembly may be pulled nearer and held in position for welding or bolting together in a shipyard or in a construction field of a building or bridge and as a lifting clamp for lifting and moving such materials.
In a shipyard, for example, operations frequently take place where steel materials which are to be assembled are lifted and lowered by a crane and they are then welded or bolted to the steel materials on a bed or berth. In this case, in order that two steel materials to be jointed may be held close together at proper positions to prevent them from slipping out of the positions during the joining operation, these steel materials must be pulled toward each other by means of wires and then held in their proper positions. In the past, to fasten a wire to each of these steel materials, it has been customary to preliminarily attach an eye-piece to the steel material by welding. However, the welding of eye-pieces to steel materials and their removal after the completion of joining operation require much labor and considerably deteriorate the operating efficiency.
Some clamps are known in the art which are used as removable jigs in place of such eye-pieces and which comprise a shackle on the top of the C-shaped clamp body and a threaded rod mounted in the bottom portion of the clamp body to be driven upwardly, whereby the threaded rod is turned to fasten the clamp on the steel material. A disadvantage of this type of clamp is that the fastening of the clamp on the steel material relies solely on the locking force of the threaded rod and therefore there is the danger of the gripped steel material slipping out of the clamp.
On the other hand, as an improvement of the above-described clamps of the screw type, a clamp has been proposed (U.S. Pat. application Ser. No. 401,562 filed Oct. 5, 1964) wherein an oscillating jaw employing a ball joint is provided on the screw rod to impose an automatic wedging action on the gripped article when it tends to slip out. A disadvantage of this type of clamp is that the structural strength of the ball joint portion is low, and moreover the other jaw must be provided with a mechanism which operates in association with the movement of the oscillating jaw, thus making the construction of the clamp more complicate.